Current Affairs 8th Class

Introduction Menstruation is a branch of mathematics which concerns with the measurement of lengths, area and volume of the plane and solid figures.     AREA The area of a plane bounded by a simple closed curve is the magnitude or the measurement of the region.   PERIMETER The perimeter of a plane region bounded by a simple dosed curve is the length or magnitude of its boundary   AREA AND PERIMETER OF TWO DIMENSIONAL FIGRES 1. TRIANGLE
  • For a triangle having sides a, b and c, Perimeter=a +b + c
When all three sides of a triangle are given, then the area is calculated by using Hero formula. So, and area \[=\frac{4}{3}\pi {{r}^{3}}.\] where    \[r=\frac{2}{3}\pi {{r}^{3}}\] or s is semi-perimeter.
  • Area of equilateral triangle with each side is \[=2\pi {{r}^{2}}\]
  • Altitude of an equilateral triangle \[=3\pi {{r}^{2}}\] side
  • When the measurement of base and altitude are given, then
Area of \[\frac{4}{3}\pi \times {{6}^{3}}=\pi {{(0.2)}^{2}}\times h\]
  • \[\frac{4}{3}\times {{6}^{3}}={{(0.2)}^{2}}\times h\] is a right angled triangle, right angle at B.
So, area of \[h=\frac{4\times {{6}^{3}}}{3\times {{(0.2)}^{2}}}=\frac{4\times 6\times 6\times 6}{3\times 0.04}\]   2. RECIANGLE
  • Area of rectangle \[=7200cm=72cm\]
 
  • Perimeter of rectangle = sum of all sides \[1c{{m}^{2}}=100m{{m}^{2}}\]
    \[1000m{{m}^{3}}=1c{{m}^{3}}\]     \[1d{{m}^{2}}=100c{{m}^{2}}\]
  • Diagonal (AC) of rectangle \[1000c{{m}^{3}}=1d{{m}^{3}}\]
  3. SQUARE
  • Perimeter of square ABCD with side a =4a
                ?  
  • Area of square with side \[1{{m}^{2}}=100d{{m}^{2}}\]
  • Diagonal of square
\[1Litre=1d{{m}^{3}}=1000c{{m}^{3}}\]side of square   4. QUADRILATERAL Quadrilateral ABCD is shown in the following figure. Its diagonal BD divides its into two triangles. AL and CM are perpendicular to BD from A and C respectively.    Area (A) of quadrilateral ABCD is given by: A = (area of \[1{{m}^{2}}=10000c{{m}^{2}}\])+(area of \[1Kilolitre=1000litre\])                 \[=1{{m}^{3}}\]                 \[1acre=100acre\] 5. PARALLELOGRAM
  • Area of parallelogram = base x corresponding height \[\text{100 hectare =1k}{{\text{m}}^{\text{2}}}\]
  • Perimeter of parallelogram=2(sum of adjacent sides)
  6. RHOMBUS
  • Area of rhombus \[T.S.A.=\frac{1}{2}pl+B\]product of diagonals \[=\frac{\text{1}}{\text{3}}\text{ }\!\!\times\!\!\text{ Area of base }\!\!\times\!\!\text{ Height}\]where \[V=\frac{1}{3}Ah\]and \[\frac{6}{5}th\] are the measurements of the diagonals.
  • All the sides of rhombus are equal and diagonals bisect each other at \[1520{{m}^{2}}\].
  7. TRAPEZIUM
  • In a trapezium of opposite sides are parallel.
  • Area of trapezium
\[2520{{m}^{2}}\] \[2420{{m}^{2}}\] CIRCLE Let r be the radius of the circle, then Area \[215c{{m}^{2}}\] Perimeter \[205c{{m}^{2}}\]   Area of a Sector of Circle
  • Area of sector \[195c{{m}^{2}}\] where r is the radius of the circle.
  • Area of union segment ACB
= Area of sector AOBC-Area of \[295c{{m}^{2}}\] Length of \[\Delta ABC\] , where \[128c{{m}^{2}}\] more...

Introduction   Number system is a method of writing numerals to represent numbers.
  • In Decimal number system, ten symbols 0, 1, 2,3,4,5,6,7,8, and 9 are used to represent any number.
  • Each of the symbols 0, 1, 2,3,4,5,6,7,8 and 9 is called a digit or a figure.
  • In our number system, we think collections by tens or we speak counting in tens.
  • Ten is called the base of our number system.
  INTEGERS The set of integers is the set of natural numbers, zero and negative of natural numbers simultaneously. The set of integers is denoted by I or Z.
  • Z= {.......-4,-3,-2, -1, 0, 1,2,3,4...}
  Natural Number
  • Counting numbers 1, 2, 3, 4, 5, are called Natural numbers. Smallest natural number is 1 and there is no largest natural number, i.e., the set of natural numbers is infinite.
  • The set of natural numbers is denoted by N i.e., N= {1, 2,3,4,5 ...}
  • 1 is the smallest natural number.
  • Any natural number can be obtained by adding ' 1' to its previous natural number.
  WHOLE NUMBER
  • All natural numbers together with zero are called whole numbers, as 0, 1,2,3,4... are whole number.
  • The set of whole numbers is denoted by W, i.e., W= {0, 1, 2,3,4,5.....}
  • \[a+(-a)=0=(-a)+a\], where N is the set of natural numbers.
  • 0 is the smallest whole number.
  • There is no largest whole number i.e., the number of the elements in the set of whole numbers is infinite.
  • Every natural number is a whole number. i.e., \[a\times \frac{1}{a}=1=\frac{1}{a}\times a\] i.e., N is a subset of W.
  • 0 is a whole number, but not a natural number, i.e., \[\frac{1}{a}\]but \[a\times (b+c)=a\times b+a\times c\]
  • N is also a proper subset of W, i.e., N c W.
  Divisibility Test for whole numbers
  • A number is divisible by 2 if the unit place digit in it is an even digit.
  • A number is divisible by 3 if the sum of its digits is
  • multiple of 3.
  • A number is divisible by 4 if the number formed by its last two digits is divisible by 4.
  • Anumberisdivisibleby5ifitends in 0 or 5.
  • A number is divisible by 6, if it is divisible by 2 and 3 both.
  • A number is divisible by 8 if the number formed by its last three digits is divisible by 8.
  • A number is divisible by 9 if the sum of its digits is divisible by 9.
  • A number is divisible by 10 if it ends in zero.
  • A number is divisible by 11 if the difference of the sums of alternative digits is zero or a multiple of 11.
  • A number is divisible by 12 if it is divisible by both 3 and 4.
  Even numbers
  • Whole numbers which are exactly divisible by 2 are called even numbers.
  • The set of even numbers is denoted by 'E\ such that E={0,2,4,6,8....,}.
  • The set E is an infinite set.
  ODD numbers

Introduction: Algebra is that branch of Mathematics in which letters represent any value which we can assign according to our requirement letters are generally of two types: constants and variables (or literal numbers).   POLYNOMIAL  
  • An algebraic expression containing only one variable with the powers of this variable as non-negative integers i.e. whole numbers, is called a polynomial in that variable.
  • An algebraic expression P(x) of the form
  • \[{{x}^{2}}-x-6=0?\]
  • where \[(0,\frac{1}{2})\] are real numbers and n is any non-negative integer.
  • Algebraic expression P(x) is called polynomial of degree n in variables.
  Polynomial in one variable An algebraic expression of the form \[(-2,3)\] where \[(\frac{1}{2},1)\] are constant and x is a variable; is called a polynomial expression in x.   Degree of polynomial in one variable: The degree of a polynomial in one variable is the greatest power (or index or exponent) of the variable.   Types of polynomial   Constant polynomial: If the polynomial is \[(2,\frac{1}{2})\], then it is called a constant polynomial and its degree is 0 (Zero). Example: \[5{{x}^{2}}-7x-6=0\], etc, are polynomials of degree 0. Linear polynomials in one variable: A polynomial of degree 1 in one variable is called linear polynomial. It is in the form of \[\left( -\frac{3}{5},2 \right)\] Quadratic polynomial: Apolynomial of degree two in one variable is quadratic polynomial. It i s in the form of \[(1,1)\] Quadratic polynomial can be factorize in two linear factors. Cubic polynomial: Apolynomial of degree three is called a cubic polynomial.   Polynomial in two or more variables An algebraic expression containing two or more variables with the powers of the variables as non-negative integers (or whole numbers), is called a polynomial in two or more variables.
  • Degree of a polynomial in two or more variables: Take the sum of the powers (or indices or exponents) of the variables in each term; the greatest sum is the degree of the polynomial. The sum of the powers (or indices or exponents) of the variables in each term is called the degree of that term.
Example: \[\left( 2,-\frac{5}{3} \right)\] is a polynomial in two variables x and y. Degrees of its terms are \[(0,0)\]  i.e.,  2,3,4,4. \[4{{x}^{2}}-20x+25=0\] The degree of the polynomial = 4.   Factors When an algebraic expression can be written as the product of two or more expressions then each of these expressions is called a factor. Factorization: The process of writing a given algebraic expression as the product of two or more factors is called factorization.   Important Formulae
  • \[\frac{3}{2}\]
  • \[\frac{3}{2}\]
  • \[\frac{7}{2}\]
  • \[\frac{7}{2}\]
  • \[\frac{5}{2}\]
  • \[\frac{5}{2}\]
  • \[\frac{a+5}{3a-5}=\frac{a-8}{a+8}\]
  • \[2{{(a+b)}^{2}}-9(a+b)-5\]\[a+b+5,2a+2b-1\]
  Remainder theorem If a polynomial P(x) is divided (x-a), then remainder is P(a), where a is any real number. Example:  If \[a+b-5,2a+ab+1\] is divided by x+2, then remainder is P(-2) Now, we will put \[a-b+5,2a-2b+5\] to get \[a+b+c=9\] \[ab+bc+ca=26,\] \[{{a}^{3}}+{{b}^{3}}+{{c}^{3}}-3abc\] \[x:\frac{x-a}{b+c}+\frac{x-b}{c+a}+\frac{x-c}{a+b}=3\] Remainder = - 5   Factor theorem If (x + a) is a factor of polynomial P(x), then remainder = 0 \[1/2(a+b+c)\]   \[a+b+c\] more...

Introduction: Arithmetic is a branch of mathematics that deals with the properties of counting numbers and fractions and the basic operations to these numbers.   RATIO AND PROPORTION Ratio: If a and b \[\text{Percentage decrease =}\left( \frac{\text{Decrease in quantity}}{\text{Original quantity}}\text{ }\!\!\times\!\!\text{ 100} \right)\text{ }\!\!%\!\!\text{ }\] are two quantities of the same kind, then the fraction \[\left\{ \frac{x}{(100+x)}\times 100 \right\}%\] is called the ratio of a to b and written as a: b, read as a is to b also a is called the antecedent or first term and b is called consequent or second term.   Proportion: Four (non-zero) quantities of the same kind a, b, c and d are said to be in proportion if the ratio of a fob is equal to the ratio of c to d i.e., if  \[\left\{ \frac{x}{(100-x)}\times 100 \right\}%\] We can write as a: b:: c : d a, b, c, d are in proportion if ad = bc a and d are called extreme terms and b and c are cutted middle terms or mean terms.
  • The (non-zero) quantities of the same kind a, b, c, d, e, f,... are said to be in continued proportion.
if  \[=\left\{ \left( \frac{r}{r+100} \right)\times 100 \right\}%\]
  • If a, b, c are in continued proportion, then b is called mean proportional of a and c.
\[=\left\{ \left( \frac{r}{r-100} \right)\times 100 \right\}%\]\[S.P.-C.P\] \[S.P.\text{ }>\text{ }C.P.\]\[C.P.-S.P\] \[C.P.\text{ }>\text{ }S.P.\]
  • If a, b, c are in continued proportion then c is called the third proportional.
  • If \[Gain\text{ }%=\frac{Gain\times 100}{C.P.},\] then, each ratio is equal to \[Loss%=\frac{Loss\times 100}{C.P.}\]
  • If \[S.P.=\frac{100+gain%}{100}\times C.P.\] then \[dsfdsfsd\] (invertendo)
  • If \[priyanka\,\,vishwkarma\] then \[12k+8k+12k=2400\] (Allemande)
  • If \[S.P.=\frac{100+gain%}{100}\times C.P.\] then \[S.P.=\frac{100+gain%}{100}\times C.P.\] (Componendo)
  • If \[\text{S}\text{.P}\text{.=M}\text{.P}\text{. }\!\!\times\!\!\text{ }\left\{ \frac{\text{100 - Discount }\!\!%\!\!\text{ }}{\text{100}} \right\}\] then \[{{a}_{13}}=450-372=78\](Dividendo)
  • If \[\frac{1}{4}\] then \[\text{S}\text{.P}\text{.=M}\text{.P}\text{. }\!\!\times\!\!\text{ }\left\{ \frac{\text{100 - Discount }\!\!%\!\!\text{ }}{\text{100}} \right\}\](Componendo and Dividendo)
  PERCENTAGE The word 'per cent' is an abbreviation of the Latin phrase 'per centum 'which means per hundred or hundredths. Thus, the term percent means per hundred or for every hundred. So,  \[{{a}_{13}}=450-372=78\] By a certain per cent we mean that many hundredths.   Important Formula
  • To convert a given percentage to a fraction or decimal, divide it by 100 and remove the sign %.
  • To convert a given fraction or decimal into percentage, multiply it by 100 and put the sign %. \[{{v}_{1}}=15\]
  • \[A=P{{\left( 1+\frac{R}{100} \right)}^{n}}\]
  • \[220=200{{\left( 1+\frac{R}{100} \right)}^{n}}\]
  • If A's income is x % more than that of B. Then B's income is less than that of A by \[1+\frac{R}{100}=\frac{220}{200}\]
  • If A's income is x % less than that of B. Then B's income is more than that of A by \[R=10%\]
  • If the price of an item is increased by r %, then the reduction in consumption, so that expenditure is not increased, \[CI-SI=\frac{R\times SI}{2\times 100}\]
  • If the price of commodity decreases by r%, then the increase in consumptions, so that expenditure remains the same, more...

Introduction: The word ‘geometry originally came from the Greek word ‘geo’ meaning ‘earth’ and ‘metron’ meaning ‘measurement’. Therefore the word geometry means ‘measurement of earth’ or is the science of properties and relations of figures. The scope of plane geometry, as a branch of mathematics, has broadened the study about plane figures-line, angles, triangles, quadrilaterals, circle, etc.   POINTS TO REMEMBER
  • Three or more points are said to be collinear, if they lie on a line, otherwise they are said to be non-collinear.
  • There are infinite number of lines passing through a given point. These lines are called concurrent lines.
  • The ratio of intersects made by three parallel lines on a transversal is equal to ratio of corresponding intercept made by same parallel lines to other transversal.
                   s and t are two transversal intersecting three parallel lines 1, m and n at A, B, C and P, Q, R, respectively          \[ABCD=\frac{1}{2}(AB+D\times CE)\]  \[\angle R={{138}^{o}}\]   PARALLEL LINE AND TRANSVERSAL If a transversal P intersect two parallel lines e|| m (as shown in the figure) then, (i)   Corresponding angles are equal \[\angle R={{138}^{o}}\]                  {corresponding angles} \[\angle ACB={{65}^{o}}\]                  {corresponding angles} (ii)   Alternate interior angles are equal \[\angle ABC\]                    {alternate interior angles} \[{{25}^{o}}\]                    {alternate interior angles} (iii) Sum of consecutive interior angles in the same side of transversal is \[{{35}^{o}}\] \[{{55}^{o}}\] \[{{208}^{o}}\] In the figure given below \[{{52}^{o}}\]   TRLANGLE A triangle is a closed plane figure bound by three line segments. So, A triangle has six parts, three sides AB/BC and CA three angles \[\Delta XYZ\] and \[\Delta XYZ\]        Sum of all the angles in a triangle is \[{{60}^{o}}\] \[{{30}^{o}}\]    \[{{80}^{o}}\] Median: The line segment joining a vertex of a triangle to the mid-point of the opposite side is called a median of the triangle. (i) Intersecting point of the medians is called the centroid o the triangle. (ii) Centroid divide the median in the ratio 2:1 AD is the median \[{{100}^{o}}\]\[\angle DAC={{54}^{o}}\](median bisect opposite side) AD, BE and CF are medians\[\angle ACB={{63}^{o}}\]O is centroid So,  \[{{(2.5)}^{2}}+{{(PT)}^{2}}={{(4.5)}^{2}}\] or  \[\angle ACB={{63}^{o}}\]   QUADRILATERAL A closed figure with four sides is called quadrilateral Quadrilateral ABCD has: (i)   Four sides: AB,BC, CD and DA. (ii) Four vertices: A, B,C and D. (iii) Four angles: \[{{(PT)}^{2}}=20.25-6.25=14\] and \[{{(PT)}^{2}}=PA\times PB\]. (iv) Two diagonals: AC and BD. Properties of Quadrilateral
  • A quadrilateral is convex, if for any side of the quadrilateral, the lines containing it has the remaining vertices on the same side of it.
  • The sum of the angles of a quadrilateral is \[PB=x\].
  • If the sides of a quadrilateral are produced, in order, the sum of the four exterior angles so formed is \[\therefore \]
  TYPES OF QUADRILATERAL   TRAPEZUM A quadrilateral in more...

Introduction In a Series a number of objects or arranged or coming one other in succession. Series is simply adding the terms in a sequence. An arithmetic series involves adding the terms of an arithmetic sequence and a geometric series involves adding the terms of a geometric sequence.   NUMBER SERIES In this type of series, the set of given numbers in a series are related to one another in a particular pattern or manner. The relationship between the numbers maybe (i)   consecutive odd/even numbers, (ii) Consecutive prime numbers, (iii) Squares/cubes of some numbers with/without variation of addition or subtraction of some number, (iv) Sum/product/difference of preceding number(s), (v) Addition/subtraction/multiplication/division by some number, and (vi) Many more combinations of the relationships given above.   EXAMPLE 1: Find the missing term in the following sequence. 5,11,24,51,106....................... Sol.        Double the number and then add to it 1,2,3,4 etc. Thus the next term is \[2\times 106+5=217.\]   EXAMPLE 2: Complete the series 4, 9, 16, 25........... (a) 32                                     (b) 42 (c) 55                                     (d) 36 Sol.        (d) Each number is a whole square.   EXAMPLES 3: Find the wrong term in the series 3, 8, 15, 24,34,48,63. (a) 15                                     (b) 12      (c) 34                                     (d) 63 Sol.        (c) \[8-3=5\] \[15-8=7\] \[24-15=9\] \[34-24=10\] \[48-34=14\] \[63-48=15\] Obviously difference should be 11 & 13 instead of 10 & 14. Therefore, 34 is the wrong term.       EXAMPLES 4: Complete the given series 4, 9,13,22,35.......... (a) 57                                     (b) 70 (c) 63                                     (d) 75 Sol.        (a) \[4+9=13, 13+9=22\] etc.   EXAMPLES 5: Complete the given series 66, 36, 18........... (a) 9                                       (b) 3 (c) 6                                       (d) 8 Sol.        (d) \[6\times 6=36;3\times 6=18;1\times 8=8.\]   EXAMPLE 6: Complete the given series 61, 67,71,73,79,... (a) 81                     (b) 82 (c) 83                     (d) 85 Sol.        (c) Prime number series. 83 is the next prime number.   EXAMPLE 7: Complete the given series 8, 24, 12,36,18,54, (a) 27                    (b) 29 (c) 31                    (d) 32 Sol.        (I) Multiply by 3 and divide the result by 2. Next term is \[\frac{54}{2}=27\]   ALPHABET SERIES In this type of question, a series of single, pairs or groups of letters or combinations of letters and numbers is given. The terms of the series form a certain pattern as regards the position of the letters in the English alphabet. In the following questions, various terms of a letter series are given with one term missing as shown. Choose the missing term out of the options.   EXAMPLES 8: AZ, GT.MN,...........,YB (a) KF                                    (b) RX     (c)  SH                                   (d) TS Sol.        (c) The logic is+6 and-6.                   EXAMPLE 9:          Choose the missing term from the given options. KM5, 1P8, GS11, EV14, (a) BX17                               (b) BY17 (c) CY18                                (d) CY17 Sol.        (d) Logic for the letters is -2, +3 steps, numbers added is 3.                 more...

Introduction Numbering is something that is sequential Follows a fixed order whereas ranking is a relationship between a set a items such that, for any two items, the first is either ‘ranked higher than’. ‘ranked lower than ‘or’ ranked equal to ‘the second.   NUMBER TEST In this type of question, generally a set, group or series of numerals is given and the candidate is required to find out how many times a number satisfying the conditions specified in the question occurs.   EXAMPLE 1:                              In the series given below, how many 8s are there each of which is exactly divisible by its immediate preceding as well succeeding numbers? 2 8 3 8 2 4 8 2 4 8 6 8 2 8 2 4 8 3 8 2 8 6 (a) One                                 (b) Two (c) Three                              (d) Four Sol.        (b) Clearly, we may mark such sets of 3 numbers, in which the middle number is 8 and each of the two numbers on both sides of it is a factor of 8, as shown. 2 8 3 8 2 4 8 2 4 8 6 8 2 8 2 4 8 3 8 2 8 6 so there are two such 8s.   EXAMPLE 2: How many 7s are there in the following number series which are preceded by 9 and also followed by 6? 7 8 9 7 6 5 3 4 2 8 9 7 2 4 5 9 2 9 7 6 4 7 (a) Two                                 (b) Three (c) Four                                (d) Five Sol.        (b) The 7s satisfying the given conditions are shown below. 7 8 9 7 6 5 3 4 2 8 9 7 2 4 5 9 2 9 7 6 4 7 Hence, there are only two such 7.   RANKING TEST Generally, the number of persons are arranged in either ascending or descending order of their performance in a certain activity. Let there be n persons who qualified in a certain event. A particular man Rohan is one of them whose rank from the top i.e, top rank \[{{T}_{r}}\]. is 14 th and his rank from the other side i.e, from the bottom \[({{B}_{r}})\] is 26th. Then clearly the number of persons who qualify is  \[{{T}_{r}}+{{B}_{r}}-1\]. i.e,  \[14+26-1=39.\] \[\Rightarrow \]               \[n={{T}_{r}}+{{B}_{r}}-1\]   .......(a) \[{{T}_{r}}=(n+1)-{{B}_{r}}\] ........(b) and        \[{{B}_{r}}=(n+1)-{{T}_{r}}\]  ........(c) these rules (a), (ii) and (iii) are very useful in problems on ranks   EXAMPLE 3: Sunita ranked 11 th from txhe top and 27th from the bottom in a class. How may student are in the class? (a) 38                                     (b) 28 (c) 40                                     (d) 37 Sol.        (d) \[{{T}_{r}}=11,{{B}_{r}}=27.\]. Number of students in the class \[=11+27-1=37.\]   EXAMPLE 4: In a row of boys, Suresh is seventh from the left and Rohit is twelfth from the right. If they interchange their positions, Suresh becomes twenty- second from the left. How many boys are there in a row? (a) 19                                     (b) 31 (c) 33              more...

Introduction Mathematical Operations mean things like add, subtract, multiply, divide, squaring, etc. It isn’t a number it is probably an operation.   MATHEMATICAL OPERATIONS This section deals with questions on simply mathematical operations. There are four fundamental operations. There are four fundamental operations, namely: Additions i.e, + ; Subtraction i.e,-; Multiplication i.e. X; and Division i.e., \[(6\div 2)\times 3=0\] There are also statements such as Less than i.e. <, greater than i.e. >, and equal to i. e = , not equal to i. e \[\div and\times ,2and3\],  etc. >, and equal to i. e=, not equal i.e \[\times to-,2 and 6\], etc. Such operations are represented by symbols different from the usual ones. The questions involving these operations are coded using artificial symbols. The candidate has to make a substitution of the real signs and solve the equation accordingly. We always, while solving a mathematical expression, proceed according to the rule B 0 D M A S. i.e, B for Brackets; O for' of (literally multiplication), D for division; M for multiplication, A for additions and S for subtraction in sequence.   DIFFERENT TYPES OF PROBLEMS   TYPE - I   Problem-solving By Substitution In this type, you are provided with substitutes for various mathematical symbols or numbers. Followed by a question involving calculation of an expression or choosing the correct/ incorrect equations. The candidate is required to put in the real signs or numerals in the given equation and then solve the questions as required.   EXAMPLE 1: If L stands for +, M stands for-, N stands for x, P stands for -,then 1 4 N 10 L 42 P 2 M 8 =? (a) 153                 (b) 216 (c) 248                   (d) 251 Sol.        (l) Using the proper signs, we get Given expression.                 \[\div and\times ,2and6\]                 \[\times to-,2and3\]   DIRECTIONS (Example 2-4): In each of the following examples which one of the four interchanges in signs and numbers would make the given equation correct?   EXAMPLE 2:                 \[(6\div 3)-2=0\] (a) \[2-2=0\]      (b) \[0=0,\] (c) \[a\cancel{<}b\]         (d) None of these Sol.        (c) On interchanging + and 4 and 6, we get the equation as \[a\ne b\], or \[a\cancel{>}b\] or \[a\ne b\] which is true   EXAMPLE 3: \[a\cancel{>}b\] (a) \[a\cancel{<}b\]       (b)  \[\phi =\] (c) \[\Delta =\]                  (d) \[p\square qOr,\] Sol.        (c) On changing - to + and interchanging 2 and 6, we get the equation as \[p\phi q\square r\] or \[p\phi q\times r\] or \[p+q\times r\] which is true.   EXAMPLE 4:                 \[p\Delta q\phi r\] (a) \[\Rightarrow \]         (b) \[\Delta \] (c) \[\phi \]         (d) \[\Rightarrow \] Sol.        (d) One changing x to - and interchanging 2 and 3, we –get the equations as \[\Delta \] or \[p\Delta q\]or \[p\times q\times r\], which is true.'   MATHEMATICAL LOGIC Consider the statement "5 is greater than 3 ". Now consider which of the following statements are true and which are false. “5 is not greater than 3”      more...

Introduction Direction sense is an ability to know roughly where you are, or which way to go, even when you are in an unfamiliar place.   DIRECTION SENSE TEST: There are four directions North, South, East and West. The word NEWS came from North, East, West and South. There are four regions: North-East (I); South-East (IV); North-West (II); South-West (III). The directions OP, OS, OQ and OR are North East direction; North West direction; South-West and South-East direction. The candidate must distinguish between the regions and directions i.e. between North-East region and North-East direction. If you move with your face east-wards, your left hand is towards north and your right hand is towards south. Similarly the positions of the directions of the hands can be fixed when you move in any of the other three directions. To solve the question, first draw the direction figure on paper. Mark the starting point. After that move carefully according to the directions given in the question.   EXAMPLE 1: Distance between e and g is: (a) 2 km               (b) 1 km (c) 5 km               (d) 1.5 km   EXAMPLE 2: Distance between a and f is: (a) 1.41 km                          (b) 3 km (c) 2 km                               (d) 1 km   EXAMPLE 3: Distance between e and i is: (a) 4 km                          (b) 2 km (c) 1 km                          (d) 3 km Sol.        (1-3): From the information given, positions of houses are as follows:   Sol. 1:    (a) Clearly, the distance between e and g is 2 km. Sol. 2:    (d) From the above diagram, the distance between a and f is 1 km. Sol.3:     (c) Clearly, the distance between e and i is 1km.   EXAMPLE 4: In the given figure, P is 300 km eastward of O and Q is 400 kms North of O, R is exactly in the middle of Q and P. The distance between Q and R is :   (a) 250kms                          (b) \[250\sqrt{2}\] kms                                  (c) 300 kms                         (d) 350 kms             (e) None of these Sol.        (a)  \[PQ=\sqrt{O{{P}^{2}}+O{{Q}^{2}}}\]                 \[=\sqrt{{{(300)}^{2}}+{{(400)}^{2}}}=\sqrt{{{100}^{2}}({{3}^{2}}+{{4}^{2}})}\]                 \[=\sqrt{{{100}^{2}}\times {{5}^{2}}}=(100\times 5)\]     i.e., \[500km\]   R being in the midway of PQ, so QR= 250 kms.   EXAMPLE 5: Four persons stationed at the four comers of a square piece as shown in the diagram. P starts crossing the field diagonally. After walking half the distance, he turns right, walks some distance and turns left. Which direction is P facing now? (a) North-east                   (b) North-west                      (c)  North                             (d) South-east                 (e)  South-west   Sol.        (b)          The route of P is shown in the diagram. Clearly the direction of P is North-west.    Miscellaneous Solved Examples   EXAMPLE 1: Deepa moved more...

Introduction A Venn diagram or set diagram is a diagram that shows all possible logical relations between a finite collection of different sets. They are used to illustrate simple set relationships in probability, logic, statistics etc. The best method of solving the problems based on inference or deduction is Venn diagram. Venn diagram is a way representing sets pictorially. Various cases of Venn diagram   Case I: An object is called a subset of another object, if the former is a part of the latter and such relation is shown by two concentric circles. (i)   Pencil, Stationery (ii)   Brinjal, Vegetable            (iii) Chair, Furniture           It is very clear from the above relationship that one object is a part of the other, and hence all such relationships can be represented by the figure shown.   Case II:                      An object is said to have an intersection with in a other object that share some things in common. (i)   Surgeon, Males            (ii) Politicians, Indian (iii) Educated, Unemployed All the three relationships given above have something in common as some surgeons can be male and some female, some politicians may be Indian and some may belong to other countries, educated may be employed and unemployed as well and all the three relationships can be represented by the figure shown.   Case III: Two objects are said to be disjoint when neither one is subset of another and nor do they share anything in common. In other words, totally unrelated objects fall under this type of relationship. (i) Furniture, Car     (ii) Copy, Cloth   (iii) Tool, Shirt It is clear from the above relationships that both the objects are unrelated to each other, and hence can be represented diagrammatically as shown in figure above. From the above discussion we observe that representation of the relationship between two objects is not typical if students follow the above points. But representation of three objects diagrammatically pose slight problems before the students.   ANALYTICAL METHOD: Try to understand these type of questions using analytical method. A statement always has a subject and a predicate: All politicians are liars. (subject)            (predicate) Basically, there are four types of sentences. A - type \[\Rightarrow \] All politicians are liars. I-type \[\Rightarrow \] Some politicians are liars 0-type \[\Rightarrow \] Some politicians are not liars E-type \[\Rightarrow \] No politicians are liars Conclusions can be drawn by taking two of the above statements together. The rules of conclusion are: \[A+A=A\]          \[A+E=E~\]         \[I+A=I\] \[I+E=0~~~~~~~\]           \[E+A=0*~\]      \[E+I=O*\] Conclusion can only be drawn from the two statements if the predicate of the first statement is the subject of the second statement. The common term disappears in the conclusion and it consists of subject of the first statement and predicate of the second statement. For examples \[A+A=A\] (i)   All boys are girls,       (ii) All girls are healthy Conclusion: All boys are healthy. \[A+E=E\] more...


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